What must be the pH of a solution that is 0.049 M Fe3+ to just cause Fe(OH)3(s) to precipitate?

Answer 1

Fe(OH)3 ==> Fe^+3 + 3OH^-

Ksp = (Fe^+3)(OH^-)^3

Substitute 0.049 for (Fe^+3) and solve for OH^-. Convert to pOH then to pH.